Alkyl (meth) acrylate copolymers

ABSTRACT

Alkyl (meth) acrylate copolymers comprising from about 10 to about 23 weight percent C 3 -C 7  alkyl (meth) acrylate; from about 77 to about 90 weight percent C 12 -C 14  alkyl (meth) acrylate(s); and from 0 to about 6 weight percent of at least one C 6 -C 20  alkyl (meth) acrylate, which provide excellent low temperature properties and shear stability to lubricating oils. The preferred embodiment comprises butyl (meth) acrylate as the C 3 -C 7  alkyl (meth) acrylate, and is essentially free from methyl (meth) acrylate.

TECHNICAL FIELD

[0001] This invention relates to novel alkyl (meth) acrylate copolymershaving excellent low temperature properties and shear stability in awide variety of base oils. The present invention also relates to the useof these copolymers as viscosity index improvers for lubricating oils.In addition, this invention demonstrates a benefit with respect tocompatibility of said VIIs with additive packages.

BACKGROUND OF THE INVENTION

[0002] Polymethacrylate (PMA) viscosity index improvers (VIIs) are wellknown in the lubricating industry. Many attempts have been made toproduce PMA VIIs that have the desired balance of high temperature andlow temperature viscometrics, as well as the required shear stabilityfor a given application. Refiners who blend with different base oilsdesire a single product that performs effectively in all of thesedifferent base oils.

[0003] The present invention is directed to novel alkyl (meth) acrylatecopolymers which exhibit excellent low temperature performance andsuperior shear stability in a wide variety of base oils. The copolymersof the present invention also demonstrate superior compatibility withother additives. While combinations of various alkyl (meth) acrylatesmay be found in viscosity index improver formulations, specific relianceon copolymers of C₃-C₇ alkyl (meth) acrylates, with the exclusion ofmethyl (meth) acrylate, leads to the novelty of the present invention.

[0004] U.S. Pat. No. 6,103,673 discloses a composition that includes avariety of poly (meth) acrylates as viscosity modifiers. The broadobjective of the '673 patent is to prepare a viscosity modifierincorporating poly (meth) acrylates having alkyl groups containing from1 to 18 carbon atoms. (Column 5, lines 29-33) Specifically, the '673patent discloses a viscosity modifier prepared using butyl (meth)acrylate as one component in a mix of poly (meth) acrylates. (Column 7,line 12) However, the '673 patent does not teach the contribution of thepresent invention, which is the primary use of C₃-C₇ alkyl (meth)acrylate copolymers and the benefit resulting from the exclusion ofmethyl (meth) acrylate, ultimately yielding a superior viscosity indeximprover.

[0005] The present invention is directed to butyl (meth) acrylatecopolymers in a viscosity index improver (VII) formulation, whereas thepreferred nitrogen-containing dispersant-type viscosity modifiers of the'673 patent are notably different. For example, the '673 patent'sspecification discloses as its preferred embodiment a compositionconsisting essentially of C₂-C₂₄ (meth) acrylates (Column 6, lines44-46), with the remaining active monomers being nitrogen-containing.The scope of the '673 patent also differs from that of the presentinvention, which additionally eliminates methyl (meth) acrylatematerials from its product to achieve superior low temperatureproperties.

[0006] U.S. Pat. No. 6,271,184 discloses an optional component ofmethacrylic acid esters containing from 2 to about 8 carbon atoms in theester group. The '184 patent presents embodiments that do not utilize amethacrylic acid component, and it is stipulated in the '184 patent thatmethyl (meth) acrylate is especially preferred. The teaching of the '184patent additionally provides that the optional component may be anitrogen-containing monomer, styrene, or substituted styrene. Whilevarious alkyl (meth) acrylate monomers are discussed in the '184 patent,the preferred use of methyl (meth) acrylate as a constituent in thecomposition does not articulate the novelty of the present invention.

[0007] Specifically, in an embodiment, the composition of the presentinvention is essentially free from methyl (meth) acrylate, in favor OfC₃-C₇ alkyl (meth) acrylate copolymers in a viscosity improverformulation.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to a novel formulation of alkyl(meth) acrylate copolymers and their use as viscosity index improversfor lubricating oils.

[0009] The alkyl (meth) acrylate copolymers of the present inventioncomprise material derived from the combining of:

[0010] (A) about 10 to about 23 weight percent C₃-C₇ alkyl (meth)acrylate copolymers;

[0011] (B) about 77 to about 90 weight percent of C₁₂-C₁₄ alkyl (meth)acrylates; and

[0012] (C) 0 to about 6 weight percent of C₁₆-C₂₀ alkyl (meth)acrylates.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention is directed, in an embodiment, to alkyl(meth) acryl ate copolymers comprising material derived from thecombining of:

[0014] (A) about 10 to about 23 weight percent C₃-C₇ alkyl (meth)acrylate copolymers;

[0015] (B) about 77 to about 90 weight percent Of C₁₂-C₁₄ alkyl (meth)acrylates; and

[0016] (C) 0 to about 6 weight percent Of C₁₆-C₂₀ alkyl (meth)acrylates.

[0017] Alkyl (meth) acryl ate copolymers of the present invention cancomprise the product, reaction product or products resulting from theprocess of combining:

[0018] (A) about 10 to about 23 weight percent C₃-C₇ alkyl (meth)acrylate copolymers;

[0019] (B) about 77 to about 90 weight percent Of C₁₂-C₁₄ alkyl (meth)acrylates; and

[0020] (C) 0 to about 6 weight percent of C₁₆-C₂₀ alkyl (meth)acrylates.

[0021] As used herein, “combining” may be used to mean the mixing,blending, contacting, free-radical polymerization, sequentialpolymerization, or anionic polymerization of elements in a composition.

[0022] Also, as used herein, a “C₃-C₇ alkyl (meth) acrylate” means analkyl ester of acrylic or methacrylic acid having a straight or branchedalkyl group of 3 to 7 carbon atoms per group, including but not limitedto, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl,isopentyl, n-hexyl, and n-heptyl monomers.

[0023] In one embodiment of the present invention, n-propyl (meth)acrylate is used as component (A). In another embodiment of the presentinvention, isopropyl (meth) acrylate is used as component (A). Inanother embodiment of the present invention, n-butyl (meth) acrylate isused as component (A). In another embodiment of the present invention,isobutyl (meth) acrylate is used as component (A). In anotherembodiment, tert-butyl (meth) acrylate is used as component (A). Inanother embodiment of the present invention, n-pentyl (meth) acrylate isused as component (A). In another embodiment, isopentyl (meth) acrylateis used as component (A). In another embodiment of the presentinvention, n-hexyl (meth) acrylate is used as component (A). In anotherembodiment, n-heptyl (meth) acrylate is used as component (A).

[0024] As used herein, “at least one C₁₂-C₁₄ alkyl (meth) acrylate”means an alkyl ester of acrylic or methacrylic acid having a straight orbranched alkyl group of 12 to 14 carbon atoms per group, including, butnot limited to, n-dodecyl, t-dodecyl, and n-tetradecyl monomers.

[0025] As used herein, “at least one C₁₆-C₂₀ alkyl (meth) acrylate”means an alkyl ester of acrylic or methacrylic acid having a straight orbranched alkyl group of 16 to 20 carbon atoms per group, including, butnot limited to, n-hexadecyl, n-octadecyl, and n-eicosyl monomers.

[0026] It is an object in an embodiment of this invention to optimizethe C₃-C₇ alkyl (meth) acrylate concentrations in the composition, andreduce or preferably eliminate methyl (meth) acrylate components. Thisenhances compatibility with additive packages while preserving desirablelow temperature and shear stability properties. Therefore, it is afurther object of this invention is to improve the composition'scompatibility with components in additive packages.

[0027] The comonomers in the alkyl groups useful in one embodiment ofthe present invention are generally prepared by standard esterificationprocedures using technical grades of long chain aliphatic alcohols.These commercially available alcohols are mixtures of alcohols ofvarying chain lengths in the alkyl groups. Consequently, for thepurposes of this invention, an alkyl (meth) acrylate is intended toinclude not only the individual alkyl (meth) acrylate product named, butalso to include mixtures of the alkyl (meth) acrylates with apredominant amount of the particular alkyl (meth) acrylate named.However, it is an objective of the present invention to reduce oreliminate methyl (meth) acrylate constituents from the composition.

[0028] In a preferred embodiment, the C₃-C₇ alkyl (meth) acrylatecopolymers of the present invention comprise the polymerization reactionproducts of (A), (B), and (C). However, those skilled in the art willappreciate that minor levels of other monomers, polymerizable withmonomers (A), (B), and (C), disclosed herein, may be present as long asthey do not adversely affect the low temperature properties of the fullyformulated fluids. Typically, additional nonspecific monomers arepresent in an amount of less than about 5 weight percent, preferably inan amount of less than 3 weight percent, most preferably in an amount ofless than 1 weight percent. In a preferred embodiment, the sum of theweight percent of (A), (B), and (C) equals 100%. Thus, as an objectiveof the present invention is to eliminate methyl (meth) acrylate from theproduct, a composition that is “essentially free” of methyl (meth)acrylate will encompass those containing trace amounts of methyl (meth)acrylate as described above.

[0029] The copolymers of the present invention may be prepared usingvarious polymerization techniques including free-radical and anionicpolymerization.

[0030] Conventional methods of free-radical polymerization can be usedto prepare the copolymers of the present invention. Polymerization ofthe acrylic and/or methacrylic monomers can take place under a varietyof conditions, including bulk polymerization, solution polymerization,usually in an organic solvent, preferably mineral oil, emulsionpolymerization, suspension polymerization and non-aqueous dispersiontechniques.

[0031] “Reaction product,” as used herein, is intended to mean thematerial resulting from the mixing, blending, contacting, reacting,polymerizing, anionic polymerizing, and/or copolymerizing of two or morematerials.

[0032] Solution polymerization is preferred. In solution polymerization,a reaction mixture is prepared comprising a diluent, the alkyl (meth)acrylate monomers, a polymerization initiator, and a chain transferagent.

[0033] In an embodiment, the diluent may be any inert hydrocarbon and ispreferably a hydrocarbon lubricating oil that is compatible with oridentical to the lubricating oil in which the copolymer is to besubsequently used. The mixture includes, e.g., from about 15 to about400 parts by weight (pbw) diluent per 100 pbw total monomers and, morepreferably, from about 50 to about 200 pbw diluent per 100 pbw totalmonomers. As used herein, “total monomer charge” means the combinedamount of all monomers in the initial, i.e., unreacted, reactionmixture.

[0034] In preparing the copolymers of the present invention byfree-radical polymerization, the acrylic monomers may be polymerizedsimultaneously or sequentially, in any order. In at least one preferredembodiment, the total monomer charge includes from 10 to 23, preferably12 to 18, weight percent of at least one C₃-C₇ alkyl (meth) acrylate; 77to 90, preferably 82 to 88, weight percent of at least one C₁₂-C₁₄ alkyl(meth) acrylate; and 0 to 6, preferably 0 to 3, weight percent of atleast one C₁₆-C₂₀ alkyl (meth) acrylate. The most preferred embodiment,presented herein, is one in which the total monomer charge comprises 12to 14 weight percent butyl (meth) acrylate, 86 to 88 weight percent ofat least one C₁₂-C₁₄ alkyl (meth) acrylate, and 0 to 3 weight percent ofat least one C₁₆-C₂₀ alkyl (meth) acrylate.

[0035] Suitable polymerization initiators include initiators whichdisassociate upon heating to yield a free radical, e.g., peroxidecompounds such as benzoyl peroxide, t-butyl perbenzoate, t-butylperoctoate and cumene hydroperoxide; and azo compounds such asazoisobutyronitrile and 2,2′-azobis (2-methylbutanenitrile). Thereaction mixture typically includes from about 0.01 wt % to about 1.0 wt% initiator relative to the total monomer mixture.

[0036] Suitable chain transfer agents include those conventional in theart, e.g., dodecyl mercaptan and ethyl mercaptan. The selection of theamount of chain transfer agent to be used is based on the desiredmolecular weight of the polymer being synthesized as well as the desiredlevel of shear stability for the polymer, i.e., if a more shear stablepolymer is desired, more chain transfer agent can be added to thereaction mixture. Preferably, the chain transfer agent is added to thereaction mixture in an amount of 0.01 to 5 weight percent, preferably0.02 to 3 weight percent, relative to the monomer mixture.

[0037] By way of example and without limitation, the reaction mixture ischarged to a reaction vessel that is equipped with a stirrer, athermometer and a reflux condenser and heated with stirring under anitrogen blanket to a temperature from about 50° C. to about 125° C.,for a period of about 0.5 hours to about 8 hours to carry out thecopolymerization reaction. In another embodiment, the copolymers may beprepared by initially charging a portion, e.g., about 25 to 60% of thereaction mixture to the reaction vessel and heating. The remainingportion of the reaction mixture is then metered into the reactionvessel, with stirring and while maintaining the temperature of the batchwithin the above describe range, over a period of about 0.5 hours toabout 8 hours. A viscous solution of the copolymer of the presentinvention in the diluent is obtained as the product of theabove-described process.

[0038] To form the lubricating oil compositions of the presentinvention, a base oil is treated with at least one of the alkyl (meth)acrylate copolymers of the present invention in a conventional manner,i.e., by adding the alkyl (meth) acrylate copolymer to the base oil toprovide a lubricating oil composition having the desired low temperatureproperties. In an embodiment of the present invention, the lubricatingoil contains from about 10 to about 23 parts by weight (pbw), preferably11 to 18 pbw, most preferably 12 to 13 pbw, of at least one of the C₃-C₇alkyl (meth) acrylates (i.e., excluding diluent oil) per 100 of themonomer mixture. In a particularly preferred embodiment, the alkyl(meth) acrylate copolymer is added to the base oil in the form of arelatively concentrated solution of the copolymer in a diluent. Therelative amount of the (meth) acrylate copolymer(s) in the concentratedVII solution of the preferred embodiment can be, for example, 80 weight%, and can be ultimately diluted to approximately 60 weight % polymerfor improved compatibility. The diluent includes any of the oilsreferred to below that are suitable for use as base oils.

[0039] FIG. 1, shown below, demonstrates that the low temperatureproperties of the present invention are best achieved using a specificrange of concentrations of C₃-C₇ (meth) acrylate in the neat copolymer.The preferred embodiment, butyl (meth) acrylate, was tested atconcentrations ranging from 7.5 weight % to 23 weight %. As shown inFIG. 1, butyl (meth) acrylate at concentrations less than 10 weight %demonstrated −40° C. Brookfield Viscosities that were in excess of10,000 (not acceptable). At concentrations greater than 18 weight %,butyl (meth) acrylate again exceeded acceptable −40° C. BrookfieldViscosity levels. In order to achieve desirable low temperatureproperties, the optimal range of concentrations for butyl (meth)acrylate fell within the range of approximately 10 weight % and 18weight %.

[0040] A final formulation containing additives and alkyl (meth)acrylate copolymers must be evaluated for compatibility of components,as well as performance as a viscosity index improver. The preferredembodiment of the present invention was further evaluated, utilizingbutyl (meth) acrylate in a concentrate of approximately 80 weight %copolymer. Ultimately a final product was diluted to a ratio in whichthe copolymer component in the VII is generally 58 weight %. The optimalweight % range for butyl (meth) acrylate in a formulation is thusevaluated based upon at least two criteria: effectiveness as a VII atlow temperatures, and degree of haziness or separation of componentswhen combined with other additives-an indicator of compatibility. Usingthe effective low-temperature range of butyl (meth) acrylateconcentrations provided by FIG. 1 (above), compatibility with additivepackages was evaluated and the results are shown in Table 1. TABLE 1Compatibility of Copolymers of Butyl (meth) Acrylate (BMA) at VaryingConcentrations of BMA with an Additive Package Number of Days BeforeSample Wt % BMA Indication of Dropout (A) 7.5 Clear after 1 month (B) 10Hazy near bottom after 1 month (C) 12.3 5 (D) 15 3 (E) 17.5 2 (F) 23.1 2

[0041] The butyl (meth) acrylate containing copolymer:additive packagecompatibility differed based upon the level of butyl (meth) acrylate inthe prepared copolymer. For example, Samples (A) and (B) were clear forlong periods of time, demonstrating successful compatibility with theadditive package. Sample (C) demonstrated acceptable compatibility,followed by a separation after five days. Samples (D), (E), and (F) werenot as compatible as preferred, having separation of the copolymer fromthe formulation in three days or less.

[0042] A comparison analysis using methyl (meth) acrylate copolymers wasperformed. Methyl (meth) acrylate is a preferred component in manyconventional poly (meth) acrylate viscosity index improvers. It is notedthat the present invention is essentially free of methyl (meth)acrylate. The comparison analysis utilized butyl (meth) acrylate at twoconcentrations, 17.5 wt % and 23.0 wt %, and methyl (meth) acrylate at17.5 wt %. Even at the higher concentration of butyl (meth) acrylate(BMA) of 23.0 wt %, less haziness and separation was shown in comparisonto the sample of methyl (meth) acrylate (MMA). Table 2 demonstratesincreased haziness and separation when the formulation incorporates MMAinstead of BMA at a cold temperature (−1° C.), room temperature, and at60° C. TABLE 2 Compatability Comparison of Copolymers with an additivepackage:Representative levels of Butyl (Meth) Acrylate to Methyl (Meth)Acrylate STORAGE DURATION AND TEMPERATURE −1° C. Room Temperature 60° C.3 Days 10 Days 3 Days 10 Days 3 Days 10 Days BMA clear slight haze clearclear clear clear (17.5 wt. %) BMA slight haze slight haze very slightvery slight clear very slight (23.0 wt. %) haze haze haze MMA hazy hazyhazy hazy hazy hazy, (17.5 wt. %) 1 mm separation

[0043] Furthermore, samples of VII formulations incorporating butyl(meth) acrylate and methyl (meth) acrylate were compared for performanceat equivalent molar concentrations. The sample of methyl (meth) acrylateachieved a Brookfield viscosity at −40° C. of >153,000 cP, exceeding the14,000 cP maximum allowed. The sample using butyl (meth) acrylateachieved a Brookfield viscosity at −40° C. of 8,480 cP, a superior andsuccessful performance. Thus, riot only is butyl (meth) acrylatedemonstrated to be more compatible with additive components, but it isalso superior in performance to methyl (meth) acrylate formulations.

[0044] The copolymers of the present invention include the preferredembodiment, butyl (meth) acrylate, as well as C₃-C₇ alkyl (meth)acrylates as described herein. As may be understood from Table 2, it isparticularly important in achieving the present invention'scompatibility with additive packages to reduce or eliminate methyl(meth) acrylate from the concentrate and lubricating oil compositions.

[0045] The copolymers of the present invention typically have a relativenumber average molecular weight, as determined by gel permeationchromatography using polymethyl methacrylate standards, between 5,000and 50,000, preferably 7,500 to 25,000.

[0046] The molecular weight of the alkyl (meth) acrylate copolymeradditive of the present invention must be sufficient to impart thedesired thickening properties to the lubricating oil. As the molecularweight of the polymers increase, the copolymers become more efficientthickeners; however, the polymers can undergo mechanical degradation inparticular applications and for this reason, polymer additives withnumber-average molecular weights (Mw) above about 50,000 are generallynot suitable for certain applications because they tend to undergo“thinning” due to molecular weight degradation resulting in loss ofeffectiveness as thickeners at the higher use temperatures (for example,at 100° C.). Thus, the molecular weight is ultimately governed bythickening efficiency, required shear stability, cost, and the type ofend-use application.

[0047] Those skilled in the art will recognize that the molecularweights set forth throughout this specification are relative to themethods by which they are determined. For example, molecular weightsdetermined by GPC, and molecular weights calculated by other methods,may have different values. It is not molecular weight per se, but thehandling characteristics and performance of a polymeric additive (shearstability, low temperature performance and thickening power under useconditions) that are important. Generally, shear stability is inverselyproportional to molecular weight. A VII additive with good shearstability (low SSI value) is typically used at higher initialconcentrations relative to another additive having reduced shearstability (high SSI value) to obtain the same target thickening effectin a treated fluid at high temperatures; the additive having good shearstability may, however, produce unacceptable thickening at lowtemperatures due to the higher use concentrations.

[0048] Conversely, although lubricating oils containing lowerconcentrations of reduced shear stability VI-improving additives mayinitially satisfy the higher temperature viscosity target, fluidviscosity will decrease significantly with use causing a loss ofeffectiveness of the lubricating oil. Thus, the reduced shear stabilityof specific VI-improving additives may be satisfactory at lowtemperatures (due to its lower concentration) but it may proveunsatisfactory under high temperature conditions. Thus, polymercomposition, molecular weight and shear stability of VI improvers mustbe selected to achieve a balance of properties that satisfy both highand low temperature performance requirements.

[0049] The finished lubricating oil composition may include otheradditives in addition to the copolymer of the present invention, e.g.,oxidation inhibitors, corrosion inhibitors, friction modifiers, antiwearagents, extreme pressure agents, detergents, dispersants, antifoamants,additional viscosity index improvers, and pour point depressants.

[0050] Base oils contemplated for use in this invention include naturaloils, synthetic oils and mixtures thereof. Suitable base oils alsoinclude basestocks obtained by isomerization of synthetic wax and slackwax, as well as basestocks produced by hydrocracking (rather thansolvent extracting) the aromatic and polar components of the crude. Ingeneral, both the natural and synthetic base oils will each have akinematic viscosity ranging from about 1 to about 40 cSt at 100° C.,although typical applications will require each oil to have a viscosityranging from about 2 to about 20 cSt at 100° C.

[0051] Natural base oils can include, but are not limited to, animaloils, vegetable oils (e.g., castor oil and lard oil), petroleum oils,mineral oils, and oils derived from coal or shale. The preferred naturalbase oil is mineral oil.

[0052] The mineral oils useful in this invention include all commonmineral oil base stocks. This would include oils that are naphthenic orparaffinic in chemical structure. Oils that are refined by conventionalmethodology using acid, alkali, and clay or other agents such asaluminum chloride, or they may be extracted oils produced, for example,by solvent extraction with solvents such as phenol, sulfur dioxide,furfural, dichlordiethyl ether, etc. They may be hydrotreated orhydrorefined, dewaxed by chilling or catalytic dewaxing processes, orhydrocracked. The mineral oil may be produced from natural crude sourcesor be composed of isomerized wax materials or residues of other refiningprocesses.

[0053] Typically the base oils will have kinematic viscosities of from 2cSt to 40 cSt at 100° C. The preferred base oils have kinematicviscosities of from 2 to 20 cSt at 100° C.

[0054] The American Petroleum Institute has categorized these differentbasestock types as follows: Group I, >0.03 wt. % sulfur, and/or <90 vol% saturates, viscosity index between 80 and 120; Group II, ≦0.03 wt. %sulfur, and ≧90 vol % saturates, viscosity index between 80 and 120;Group III, ≦0.03 wt. % sulfur, and ≧90 vol % saturates, viscosityindex >120; Group IV, all polyalphaolefins.

[0055] Group II and Group III basestocks are typically prepared fromconventional feedstocks using a severe hydrogenation step to reduce thearomatic, sulfur and nitrogen content, followed by dewaxing,hydrofinishing, extraction and/or distillation steps to produce thefinished base oil. Group II and III basestocks differ from conventionalsolvent refined Group I basestocks in that their sulfur, nitrogen andaromatic contents are very low. As a result, these base oils arecompositionally very different from conventional solvent refinedbasestocks. Hydrotreated basestocks and catalytically dewaxedbasestocks, because of their low sulfur and aromatics content, generallyfall into the Group II and Group III categories. Polyalphaolefins (GroupIV basestocks) are synthetic base oils prepared from various alphaolefins and are substantially free of sulfur and aromatics.

[0056] Synthetic base oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as oligomerized, polymerized, and interpolymerizedolefins (such as polybutylenes, polypropylenes, propylene, isobutylenecopolymers, chlorinated polylactenes, poly(1-hexenes), poly(1-octenes)and mixtures thereof); alkylbenzenes (including dodecyl-benzenes,tetradecylbenzenes, dinonyl-benzenes and di(2-ethylhexyl)benzene);polyphenyls (such as biphenyls, terphenyls and alkylated polyphenyls);and alkylated diphenyl ethers, alkylated diphenyl sulfides, as well astheir derivatives, analogs, and homologs thereof, and the like. Thepreferred synthetic oils are oligomers of alpha-olefins, particularlyoligomers of 1-decene, also known as polyalpha olefins or PAO's.

[0057] Synthetic base oils also include alkylene oxide polymers,interpolymers, copolymers, and derivatives thereof where the terminalhydroxyl groups have been modified by esterification, etherification,etc. This class of synthetic oils is exemplified by: polyoxyalkylenepolymers prepared by polymerization of ethylene oxide or propyleneoxide; the alkyl and aryl ethers of these polyoxyalkylene polymers(e.g., methyl-polyisopropylene glycol ether having an average molecularweight of 1000, diphenyl ether of polypropylene glycol having amolecular weight of 100-1500); and mono- and poly-carboxylic estersthereof (e.g., the acetic acid esters, mixed C₃-C₈ fatty acid esters,and C₁₂ oxo acid diester of tetraethylene glycol).

[0058] Another suitable class of synthetic lubricating oils comprisesthe esters of dicarboxylic acids (e.g., phthalic acid, succinic acid,alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaicacid, subric acid, sebasic acid, fumaric acid, adipic acid, linoleicacid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids,etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol,dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethyleneglycol monoethers, propylene glycol, etc.). Specific examples of theseesters include dibutyl adipate, diisobutyl adipate, di(2-ethylhexyl)sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl phthalate,diisooctyl azelate, diisooctyl adipate, diisodecyl azelate, didecylphthalate, diisodecyl adipate, dieicosyl sebacate, the 2-ethylhexyldiester of linoleic acid dimer, and the complex ester formed by reactingone mole of sebasic acid with two moles of tetraethylene glycol and twomoles of 2-ethyl-hexanoic acid, and the like. A preferred type of oilfrom this class of synthetic oils are adipates of C₄ to C₁₂ alcohols.

[0059] Esters useful as synthetic base oils also include those made fromC₅ to C₁₂ monocarboxylic acids and polyols and polyol ethers such asneopentyl glycol, trimethylolpropane pentaerythritol, dipentaerythritol,tripentaerythritol, and the like.

[0060] Silicon-based oils (such as the polyalkyl-, polyaryl-,polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) compriseanother useful class of synthetic lubricating oils. These oils includetetra-ethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl) silicate,tetra-(p-tert-butylphenyl) silicate,hexa-(4-methyl-2-pentoxy)-disiloxane, poly(methyl)-siloxanes and poly(methylphenyl) siloxanes, and the like. Other synthetic lubricating oilsinclude liquid esters of phosphorus containing acids (e.g., tricresylphosphate, trioctylphosphate, and diethyl ester of decylphosphonicacid), polymeric tetra-hydrofurans, poly-Ε-olefins, and the like.

[0061] Lubricating oil compositions of the present invention comprisingthe alkyl (meth) acrylate copolymers of the present invention may beused in numerous applications including gear lubrication, automatictransmission fluids, continuously variable transmission fluids, manualtransmission fluids, hydraulic fluids, crankcase applications and shockabsorber fluids.

[0062] Depending upon the intended end use of the lubricating oilformulations and the compositions of the present invention, the shearstability of the inventive acrylate copolymer can be adjusted bycontrolling the amount of initiator and/or chain transfer agent presentin the polymerization reaction mixture.

[0063] For example, in automatic transmission fluid applications it maybe desired to have a highly shear stable lubricating fluid. In anembodiment of the present invention, automatic transmission fluids areprepared by adding to a base oil a copolymer of the present inventionand a detergent/inhibitor package such that the fluids have a percentshear stability index (SSI) as determined by the 20 hour Tapered BearingShear Test in the range of 1% to about 80%, preferably 1 to 20%. The 20hour Tapered Bearing Shear Test is a published standard test entitled“Viscosity Shear Stability of Transmission Lubricants” and is describedin CEC L-45-T-93 (Taper Roller Bearing) and is also published as DIN 51350, part 6, said publication being incorporated by reference herein inits entirety.

[0064] The general procedure used to prepare the butyl (meth) acrylatepolymer, the preferred embodiment of the present invention, was asfollows: To a 2 liter resin kettle fitted with an overhead stirrer, athermocouple, a sparge tube, and a condenser was charged the monomer andthe reaction oil. The stirrer was set at 300 rpm and the temperature wasincreased to 40° C. The sparge tube was replaced with a nitrogen blanketand the temperature was increased to about 78° C. Then, lauryl (dodecyl)mercaptan as a chain transfer agent was then added, followed by AIBN(azobisisobutyronitrile). The mixture was heated and stirred for 4 hoursat 78° C. The temperature was then increased to about 104° C. for 1.5hours to decompose any residual catalyst. Diluent oil was added toarrive at 58% polymer solution by weight and stirring and heatingcontinued at about 70-80° C. for 1 hour. The reactor was cooled and thediluted polymer was then stored at room temperature until testing.

[0065] After preparing the copolymers and fluids in embodiments of thepresent invention, a final formulation may be produced that exceeds thecapabilities known or expected in the art. As shown below in Table 3, acommercially available VII product, Viscoplex™ 0-030, was compared anembodiment of the present invention prepared as described herein. Thepreferred embodiment of the present invention, butyl (meth) acrylate(BMA) copolymers, demonstrated compatibility with a standard additivepackage as well as improved performance. Table 3 demonstrates thesuperior low temperature properties of the BMA copolymers of the presentinvention, wherein the two lubricant compositions were tested using theidentical type and amount of additive package. No pour point depressantwas added. The low temperature properties of these fluids were testedaccording to ASTM D 2983, which is incorporated herein by reference.TABLE 3 Test Performance of Butyl (Meth) Acrylate Compared to aCompetitive Product Viscoplex ™ BMA 0-030 TESTING LIMITS KinematicViscosity, 100 C 7.17 7.06 7.0 cSt min (cSt) Kinematic Viscosity, 40 C33.53 33.21  40 cSt max (cSt) Pour Point (C) −45 −48 −45 C maxBrookfield @ −40C (cP) 8480 15720 14000 cP max Brookfield @ −30C (cP)2660 4120  3300 cP max 20 hour KRL, % viscosity 2.95 5.53 minimize loss

[0066] It is clear that lubricant formulation comprising the viscosityindex improver of the present invention exhibits superior lowtemperature properties compared to polymethacrylate viscosity indeximprover outside the scope of the present invention, as evidenced by thesuperior results in Table 3. Specifically, the inventive sampleexhibited a Brookfield viscosity at −40C of 8480 cps (a “pass”) versusthe 15,720 cps (a “fail”) for the commercially available Viscoplex0-030™, which was selected for comparison. Similarly, the inventiveexample exhibited a Brookfield viscosity at −30C of 2660 cps (a “pass”)versus the 4120 cps (a “fail”) of the Viscoplex 0-030™.

[0067] This invention is susceptible to considerable variation in itspractice. Accordingly, this invention is not limited to the specificexemplifications set forth hereinabove. Rather, this invention is withinthe spirit and scope of the appended claims, including the equivalentsthereof available as a matter of law.

[0068] The patentees do not intend to dedicate any disclosed embodimentsto the public, and to the extent any disclosed modifications oralterations may not literally fall within the scope of the claims, theyare considered to be part of the invention under the doctrine ofequivalents.

I claim:
 1. An alkyl (meth) acrylate copolymer comprising: (A) about 10 to about 23 weight percent of at least one C₃-C₇ alkyl (meth) acrylate; (B) about 77 to about 90 weight percent of at least one C₁₂-C₁₄ alkyl (meth) acrylate; and (C) 0 to about 6 weight percent of at least one C₁₆-C₂₀ alkyl (meth) acrylate.
 2. An alkyl (meth) acrylate copolymer product obtained by combining components comprising: (A) from about 10 to about 23 weight percent of at least one C₃-C₇ alkyl (meth) acrylate; (B) from about 77 to about 90 weight percent of at least one C₁₂-C₁₄ alkyl (meth) acrylate; and (C) 0 to about 6 weight percent of at least one C₁₆-C₂₀ alkyl (meth) acrylate.
 3. The copolymer of claim 1 or claim 2, wherein the copolymer is essentially free from methyl (meth) acrylate units.
 4. The copolymer of claim 1 or claim 2, wherein the C₃-C₇ alkyl (meth) acrylate is butyl (meth) acrylate.
 5. The copolymer of claim 1 or claim 2, wherein the copolymer has an average molecular weight number from about 5,000 to about 50,000.
 6. A method for making a lubricating oil, comprising adding to an oil of lubricating viscosity a copolymer according to claim 1 or claim
 2. 7. A lubricating oil composition comprising: (A) an oil of lubricating viscosity; and (B) a copolymer according to claim 1 or claim
 2. 8. The lubricating oil composition of claim 7, wherein the C₃-C₇ alkyl (meth) acrylate is butyl (meth) acrylate.
 9. The lubricating oil composition of claim 7, wherein the composition is essentially free from methyl (meth) acrylate units.
 10. The lubricating oil composition of claim 7, wherein component (B) is present in an amount of from 1 to about 30 parts by weight of active copolymer per 100 parts by weight of oil in a final composition.
 11. The lubricating oil composition of claim 7 further comprising at least one additive selected from the group consisting of oxidation inhibitors, corrosion inhibitors, friction modifiers, antiwear agents, extreme pressure agents, detergents, dispersants, antifoamants, additional viscosity index improvers, and pour point depressants.
 12. A method for improving the low temperature properties of an oil, said method comprising adding to an oil of lubricating viscosity a copolymer according to claim 1 or claim
 2. 13. A method for improving the compatibility of a lubricating oil containing additive components, said method comprising adding to an oil of lubricating viscosity at least one additive component, and a copolymer according to claim 1 or claim
 2. 14. A method for improving the viscosity index of a lubricating oil, said method comprising adding to an oil of lubricating viscosity a copolymer according to claim 1 or claim
 2. 15. A gear lubricant composition comprising: (A) an oil of lubricating viscosity; and (B) a copolymer according to claim 1 or claim
 2. 16. The gear lubricant composition of claim 15, wherein the C₃-C₇ alkyl (meth) acrylate is butyl (meth) acrylate.
 17. The gear lubricant composition of claim 15, wherein the copolymer is essentially free from methyl (meth) acrylate.
 18. The gear lubricant composition of claim 15, wherein component (B) is present in an amount of 1 to about 30 by weight of active copolymer by weight in said gear lubricant composition.
 19. A composition for an automatic transmission fluid comprising: (A) an oil of lubricating viscosity; (B) a copolymer according to claim 1 or claim 2; and (C) at least one additive selected from the group consisting of oxidation inhibitors, corrosion inhibitors, friction modifiers, antiwear agents, extreme pressure agents, detergents, dispersants, antifoamants, viscosity index improvers, and pour point depressants.
 20. A method for lubricating a continuously variable transmission, comprising applying thereto the composition of claim
 19. 21. The composition of claim 19, wherein the automatic transmission fluid has a percent shear stability index, as determined by the 20 hour Tapered Bearing Shear Test, in the range of 1% to about 80%.
 22. The composition of claim 19, wherein said automatic transmission fluid has a percent shear stability index, as determined by the 20 hour Tapered Bearing Shear Test, in the range of 1% to 20%.
 23. The composition of claim 19, wherein the transmission fluid is a continuously variable transmission fluid.
 25. A vehicle comprising an automatic transmission lubricated with the composition of claim
 19. 25. An automatic transmission lubricated with the composition of claim
 19. 26. The automatic transmission of claim 25, wherein the transmission is a continuously variable transmission.
 27. The copolymer of claim 1, wherein component (A) is present in an amount of about 11 to about 18 weight percent.
 28. The copolymer of claim 1, wherein component (A) is present in an amount of about 12 to about 13 weight percent. 